Resin-molded stator, a method of manufacturing the same, and a rotary machine using the same

ABSTRACT

A highly reliable resin-molded stator not suffering insulation breakdown between different phases of stator coils even when the operation mode is repeated where the output of a rotary machine using a resin-molded stator is to be increased from the level under a stopped status to the maximum achievable level within a short time. Also provided are methods of manufacturing such a stator, and a rotary machine using the same. The a resin-molded stator of the invention comprises a stator core, electrically insulated stator coils wound around the plurality of slots or protrusions provided in the axial direction of the stator core, and molding resin with which are molded the stator core and the stator coils located at the aforementioned slots or protrusions. At the stator core end, non-adhesive structure is established between the molding resin and at least one of the end faces of the stator core.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resin-molded stator, a method ofmanufacturing the same, and a rotary machine using the same.

2. Description of the Prior Art

Conventional resin-molded stators and rotary machines using the sameemploy the structure where, as disclosed in Japanese Application PatentLaid-Open Publication No. 08-223866, Japanese Application PatentLaid-Open Publication No. 09-157440, and Japanese Application PatentLaid-Open Publication No. 10-51989, the stator coil wound around theplurality of slots or bumps in the stator core, and the stator coil atthe end of the stator core are molded with resin and the molding resinand the end of the stator core that faces in the axial direction of therotary machine are bonded. Also, an alternating-current (AC) powergenerator using brushes to supply power to the rotor is disclosed inJapanese Application Patent Laid-Open Publication No. 2000-125513.

The present inventors have found that the prior art practice poses theproblem that when a stringent acceleration test simulating the operationmode in which the output of the rotary machine is to be increased fromthe level under its stopped status to the maximum achievable levelwithin a short time is repeated several times, insulation breakdownoccurs between the stator coils and the ground or between the differentphases of the stator coils. It is considered that the insulationbreakdown occurs as follows:

It has been examined why and how the insulation breakdown occurs betweenthe stator coils and the ground or between the different phases of thestator coils when the operation mode in which the output of the rotarymachine is to be increased from the level under its stopped status tothe maximum achievable level within a short time is repeated severaltimes. As a result, it has been found that when the output level isincreased to its maximum within a short time, the stator coils areheated by the electrical resistance of the coil conductor and, dependingon the particular conditions, the coil temperature increases to amaximum of about 250° C. At the same time, it has also been found thatsince the heat capacity of the stator core is high, increases in thetemperature thereof retard with respect to the stator coils.Accordingly, the difference in temperature between the stator coils andthe stator core often reaches 200° C. or more.

The thermal expansion coefficient of the copper used for the statorcoils is 1.7×10⁻⁵ 1/° C., and the thermal expansion coefficient of thestator core in the direction that electromagnetic steel plates werelaminated in the direction of the rotational axis of the stator core toform the core is about 1.3×10⁻⁵ 1/° C. In this way, the stator coils andthe stator core differ in thermal expansion coefficient, and when atemperature difference exists between the stator coils and the statorcore, the amount of thermal elongation also differs between both. Theresin-molded stator may have the structure where one side of its coilend is constrained by being positioned between the stator core and theend face of the housing in the direction of its rotational axis in therotary machine. The relative displacement Δ occurring between the statorcoils and the stator core, at the coil end of a resin-molded statorhaving such structure, is represented by formula (1) below.Δ={αc×(Tc−Tr)−αf×(Tf−Tr)}×L  (1)where: “αc” and “αf” are the thermal expansion coefficients of thestator coils and the stator core, respectively; “Tc” and “Tf” are thetemperatures of the stator coils and stator core when the output of therotary machine is increased to the maximum output level within a shorttime; “Tr” is the temperature at which the difference between the statorcoils and the stator core in terms of thermal elongation is zero, and;“L” is the laminating thickness of the stator core.

For example, if the laminating diameter of the stator core in aresin-molded stator having the structure where one side of its coil endis constrained by being positioned between the end face of the housingand the stator core is 100 mm, when the temperature of the stator coilsincreases from 20° C. to 230° C. and the temperature of the stator coreincreases from 20° C. to 50° C., the relative displacement Δ occurringbetween the stator coils and stator core at the coil end can becalculated by assigning, to formula (1) shown above, an “αc” value of1.7×10⁻⁵ 1/° C. as the thermal expansion coefficient of the statorcoils, an “αf” value of 1.3×10⁻⁵ 1/° C. as the thermal expansioncoefficient of the stator core, a “Tc” value of 230° C. as thetemperature of the stator coils, a “Tf” value of 50° C. as thetemperature of the stator core, a “Tr” value of 20° C. as thetemperature at which the difference between the stator coils and thestator core in terms of thermal elongation is zero, and an “L” value of100 mm as the laminating thickness of the stator core. As a result, itfollows from the difference in thermal elongation that the relativedisplacement Δ occurring between the stator coils and stator core at thecoil end is 0.35 mm.

The stress “σc” applied to the stator coil section when the spacebetween the stator core and the stator coils is constrained so as not tocause relative displacement between both can be represented using thefollowing formula (2) which assumes that all thermal strain is imposedon the stator coils:σc=Δ×Ec/L  (2)where “Δ” is the relative displacement between the stator coils andstator core at the coil end, “Ec” is the longitudinal elastic modulus ofthe stator coils, and “L” is the laminating thickness of the statorcore.

If “Δ”, “Ec”, and “L” are 0.35 mm, 100 GPa, and 100 mm, respectively,the stress “σc” applied to the stator coils reaches 0.35 GPa.

The stator coils running through the stator slots and emerging at thecoil end are split into sections wound clockwise and counterclockwisearound the stator core according to phase and engage with other statorslots. Accordingly, the coils wound from a plurality of stator slotstowards other stator slots are accommodated under a mutual contactstatus at the coil end section of the stator. In this case, if thestator core and the resin-molded section at the coil end are bonded, athermal elongation difference reaching 0.35 mm occurs between the statorcore and stator coils at the coil end, and at the same time, since thestator coils emerging at the coil end are wound in different directionsfor each phase, a phase shift occurs between the coils of differentphases and is likely to damage the insulation around the conductors,resulting in insulation breakdown. The same also applies toconcentrated-winding structure having coils wound at the protrusions ofthe stator core. That is to say, if the stator core and the resin-moldedsection at the coil end are bonded, the difference in thermal elongationbetween the conductors and the core due to abrupt increases in thetemperature of the conductors causes the buckling thereof and is likelyto damage the insulation, and resulting in insulation breakdown.

SUMMARY OF THE INVENTION

The object of the present invention is to provide

-   -   a resin-molded stator in which the stator coils wound around a        plurality of slots and the stator coils at the end of the stator        core are molded with resin in order for insulation breakdown        between the stator coils and the ground or between the different        phases of the stator coils to be prevented by repeating several        times the operation mode in which the output level of a rotary        machine employing the aforementioned resin-molded stator is to        be increased from the level under a stopped status to the        maximum level within a short time, a method of manufacturing the        resin-molded stator outlined above, and a rotary machine using        the same.

The present invention applies to a resin-molded stator comprising

a stator core,

stator coils wound around said stator core and provided with insulation,and

molding resin with which the stator core and said stator coils aremolded,

wherein said resin-molded stator is characterized in that said moldingresin has non-adhesive structure against at least one of the end facesof the stator core. The particles of aluminum oxide, magnesium oxide,silicon oxide, boron nitride, calcium carbonate, talc, or the like areadded as an inorganic filler to the molding resin.

The resin-molded stator pertaining to the present invention is furthercharacterized in that a non-adhesive film or separator for obtainingnon-adhesion against said resin is formed as non-adhesive structurebetween said molding resin and at least one of said end faces of thestator core. Polytetrafluoroethylene, polyvinylidene fluoride, polyvinylfluoride, and the like are used in bridged form as the non-adhesivefilm, and this film is not fusible with respect to the aforementionedmold. Or silicon is used as the separator.

In other words, in the present invention, the resin-molded stator wherethe stator coils provided with insulation are wound around the pluralityof slots or protrusions provided in the axial direction of the statorcore and the stator core, the stator coils around the slots orprotrusions, and the stator coils at the stator core end, ischaracterized in that non-adhesive structure is provided between themolding resin and said end face of the stator core.

A rotary machine may need to be operated at its maximum output level atthe same time the machine is started. When the rotary machine isactually placed in such operation, the temperature of its stator coilswill increase to about 250° C. by the action of Joule heat. However,since the stator core has a large heat capacity, increases in thetemperature of the stator core are retarded with respect to the statorcoils by the thermal resistance of the electric insulating materiallocated between the stator coils and the stator core, and for thisreason, the temperature of the stator core often reaches only about 50°C., even when the temperature of the stator coils reaches 250° C. In thepresent invention, the differences in the amount of thermal elongationthat result, at that time, from the thermal expansion coefficient of thestator core in the laminating direction of electromagnetic steel platesin the direction of the rotational axis of the stator core, from thedifference in temperature between and the stator coils and the statorcore, and from the difference in thermal expansion coefficient betweenboth, are absorbed by providing non-adhesive structure between themolding resin and the end face of the stator core so as to prevent coildamage.

It is preferable that the above-mentioned molding resin should be madeof the polyester-based resin containing an inorganic filler, that theinorganic filler should contain calcium carbonate and aluminum oxide,and that the above-mentioned non-adhesive film should bepolytetrafluoroethylene resin.

The present invention also applies to a resin-molded statormanufacturing method characterized in that

it sequentially comprises a process in which stator coils provided withinsulation are to be wound around a plurality of slots or protrusionsformed in the axial direction of a stator core consisting of laminatedelectromagnetic steel plates, and a process in which the end face ofsaid stator core is to be axially provided with a resin film orseparator having the same shape as that of the vertical section of thestator core,

and further characterized in that said manufacturing method sequentiallycomprises a process in which, after the above-described process, thestator core around which said stator coils are wound is to be built intoa housing, a process in which the aforementioned housing with the statorcore built thereinto is to be preheated and then set in a preheatedmold, and a molding process in which the stator core and the statorcoils located at the above-mentioned slots or protrusions and at the endof the stator core are to be molded with resin by injecting the resininto the mold having the housing set therein.

In addition, in the present invention, by providing, between the housingof the rotary machine and the molding resin at the coil end where thestator coils were molded, insert structure in which the housing and themolding resin can be moved in the respective axial directions and cannotbe moved about the respective axes, it is possible to suppress thevibrational displacement associated with operation that occurs betweenthe stator coil at the stator slot portion and the stator coil at theresin-molded coil end portion, and hereby to prevent stator coil damage.

If the size (W) of a space formed in the axial direction of the rotarymachine, between the coil end portion provided with resin molding byproviding non-adhesive structure with respect to the end face of thestator core, is smaller than the value derived from the product of(A×T×Lc) [A is the thermal expansion coefficient of the stator coilconductor, T is the maximum temperature that the conductor reachesduring the operation of the rotary machine, and Lc is the total axiallength of the conductor that includes said coil end], when thetemperature of the conductor increases, the coil end portion providedwith non-adhesive structure with respect to the end face of the statorcore will come into contact with the components mounted at the end plateand consequently the effect that should originally be obtainable byproviding the non-adhesive structure will not be created. This problem,however, can be solved by setting the size (W) of the above-mentionedspace to a value equal to, or greater than, the value derived from theabove-mentioned value of (A×T×Lc).

The rotary machine pertaining to the present invention is characterizedin that the rotary machine comprises a rear plate for covering the otherside of said rotor, a brush assembly for supplying electric power viaslip rings provided on the rotor, a rear bracket connected to said rearplate and intended for covering the brush assembly, a bearing whichsupports one end of the rotor and is provided in the housing, and abearing which supports the other end of said rotor and is provided inthe rear plate.

The rotary machine pertaining to the present invention is furthercharacterized in that the rotary machine comprises an end plate forcovering the other side of said rotor, a bearing which supports one endof said rotor and is provided in said housing, and a bearing whichsupports the other end of said rotor and is provided in said end plate.

It is preferable that the sections of the above-mentioned housing thatare to accommodate the resin-molded stator and one side of the rotorbuilt into the stator should be formed into a single unit, that a spacefor absorbing the thermal expansion of the stator coils in their axialdirection should be provided at the side having the non-adhesivestructure described above, that the above-mentioned should be providedbetween the molding resin of the stator coils and the rear plate orbetween the molding resin of the stator coils and the end plate, andthat there should be insert structure in which the axial length of thehousing at its inner circumferential side should be greater than theaxial length of the resin-molded stator and the housing and the moldingresin separated from the stator core by the non-adhesive structureprovided at the core end of the stator can be moved in the respectiveaxial directions and cannot be moved about the respective axes.

According to the present invention, it is possible not only to provide ahighly reliable resin-molded stator not suffering insulation breakdownbetween the different phases of the stator coils even when the operationmode for increasing the output of a rotary machine from the level underits stopped status to the maximum achievable level within a short timeis repeated, but also to provide a rotary machine that uses such astator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the resin-molded stator pertainingto the present invention;

FIG. 2 is a cross-sectional view of the section A–A′ in FIG. 1;

FIG. 3 is a partial cross-sectional view of the rotary machinepertaining to the present invention;

FIG. 4 is a partial side view of a conventional rotary machine;

FIG. 5 is a partial cross-sectional view of the rotary machine whichemploys concentrated winding in the resin-molded stator pertaining tothe present invention.

FIG. 6 is a partial cross-sectional view of a brushless rotary machineusing the resin-molded stator which employs concentrated winding of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

FIG. 1 is a cross-sectional view of the resin-molded stator showing anembodiment of the present invention. FIG. 2 is a cross-sectional view ofthe section A–A′ in FIG. 1, and FIG. 3 is a cross-sectional view of thesection B–B′ in FIG. 2. The steps taken to manufacture this resin-moldedstator are described below. A slot provided in a stator core 1consisting of laminated electromagnetic steel plates is covered with aliner 8 which is made of a polyamideimides non-woven fabric, and thenstator coils 2 each consisting of a conductor provided with insulationare wound around the stator core 1. After this, the stator core 1 aroundwhich the stator coils 2 have been wound is built into a housing 4 whichhas a bearing installation recess 3 at the end of the housing. Of thetwo surfaces vertical to the axis of the stator core 2, only the surfacelocated at the opposite side to the bearing installation recess 3 in thehousing 4 when the stator core 1 is to be built into the housing iscoated with a polytetrafluoroethylene resin film which has beenpre-processed into the same shape as that of the electromagnetic steelplates of the stator core 1, and the coated surface mentioned abovefunctions as a non-adhesive treatment section 5 to prevent bondingbetween the stator core 1 and the molding resin 7 to be later added.

The polytetrafluoroethylene resin film is bridged, does not fuse duringmolding, and functions as non-adhesive structure. Although, in thepresent embodiment, the resin film is formed as a non-adhesive treatmentsection 5 between molding resin and stator core at one side, this filmcan also be provided at both sides. In the present embodiment, as shownin FIG. 1, since the resin film also functions as a mold forresin-molding the housing 4 located at one side, this film givesnon-adhesiveness to one side. In the housing 4, a plurality ofinjection-molding gate positions 10 functioning as resin injection portsfor resin-molding the housing 4 are provided circumferentially on theside thereof so as to ensure equal injection of the resin, and thesegates are filled with the molding resin. Molds are provided at theopposite side to the resin injection ports and at the innercircumferential side.

The housing 4 is also provided with an agency 6 through which thecoolant for cooling the rotary machine is to be passed. Next, thehousing 4 into which the stator core 1 with the stator coils 2 woundaround it, is preheated to 100° C. and then set in a mold which has beenheated to 150° C. beforehand. After this, the polyester-based moldingresin that has been filled with the powder of calcium carbonate andaluminum oxide is injection-molded at a pressure of 4 MPa, and hereby,the stator coil 2 inside the slot of the stator core 1 and the statorcoil 2 at the coil end emerging from the stator core 1 are molded. Asshown in FIG. 2, a recess 9 for preventing the rotational vibration ofthe coil end portion is provided in the housing 4.

Two types of resin are available as examples of the polyester-basedmolding resin mentioned above: (1) molding resin created by mixingresin, calcium carbonate powder, and alumina powder at the weight rateof 1:1:1, with the resin consisting of 100 weight parts of maleicacid-containing unsaturated polyester and 40 weight parts of styrenemonomer, and (2) molding resin created by mixing resin, calciumcarbonate powder, and alumina powder at the weight rate of 1:1:1, withthe resin consisting of 100 weight parts of isophthalic acid-containingunsaturated polyester and 40 weight parts of styrene monomer.

FIG. 4 is a cross-sectional view of the rotary machine pertaining to thepresent invention. A rotor 19 and a shaft 21 having slip rings 20 builtthereinto are attached to the resin-molded stator shown in FIG. 1. Afterthis, rear plates 23 which have a diode 22 and the like, are attached,then a brush assembly 24 and a regulator 25 are installed, and a rearbracket 26 is installed. The axial length (W) of a coil end space 28provided between the resin-molded section at the coil end portion andthe rear plate 23 is set to a value equal to, or greater than, the valuederived from the product of (A×T×Lc), where A is the thermal expansioncoefficient of the stator coil conductor, T is the maximum temperaturethat the conductor reaches during the operation of the rotary machine,and Lc is the total axial length of the conductor that includes saidcoil end.

A stringent acceleration test for increasing the output of thethus-manufactured rotary machine from the level under its stopped statusto the maximum achievable level within a short time has been repeatedfive times, with the result that no abnormality has been observed.Although an example of a rotary machine with slip rings, a brushassembly, and a diode, has been shown in the present embodiment, it isobvious that the embodiment can be similarly applied to a rotary machinenot equipped with these components.

COMPARATIVE EXAMPLE 1

FIG. 5 is a cross-sectional view of the resin-molded stator shown as acomparative example against the present invention. The steps taken tomanufacture this resin-molded stator are described below. A slotprovided in a stator core 1 consisting of laminated electromagneticsteel plates is covered with a liner which is made of a polyamideimidesnon-woven fabric, and then stator coils 2 each consisting of a conductorprovided with insulation are wound around the stator core 1. After this,the stator core 1 around which the stator coils 2 have been wound isbuilt into a housing 4 which has a bearing installation recess 3 at theend of the housing. Or the housing 4 is provided with an agency 6through which the coolant for cooling the rotary machine. Next, thehousing 4 into which the stator core 1 with the stator coils 2 woundaround it, is preheated to 100° C. and then set in a mold which has beenheated to 150° C. beforehand. After this, the polyester-based moldingresin that has been filled with the powder of calcium carbonate andaluminum oxide is injection-molded at a pressure of 4 MPa, and hereby,the stator coil 2 inside the slot of the stator core 1 and the statorcoil 2 at the coil end emerging from the stator core 1 are molded.

A rotor 19 and a shaft 21 having slip rings 20 built thereinto areattached to the resin-molded stator. After this, rear plates 23 whichhave a diode 22 and the like, are attached, then a brush assembly 24 anda regulator 25 are installed, and a rear bracket 26 is installed.

A stringent acceleration test for increasing the output of thethus-manufactured rotary machine from the level under its stopped statusto the maximum achievable level within a short time has been repeatedfive times, with the result that insulation breakdown has occurredbetween phases.

Embodiment 2

FIG. 6 is a partial cross-sectional view of a brushless rotary machineusing the resin-molded stator which employs concentrated winding in thepresent invention. The steps taken to manufacture this rotary machineare described below. A protrusion provided on a stator core 1 consistingof laminated electromagnetic steel plates is covered with a liner whichis made of a polyamideimides non-woven fabric, and then stator coils 2each consisting of a conductor provided with insulation are wound aroundthe stator core 1. After this, the stator core 1 around which the statorcoils 2 have been wound is built into a housing 4. Of the two surfacesvertical to the axis of the stator core 2, only the surface located atthe opposite side to the bearing installation recess in the housing 4when the stator core 1 is to be built into the housing is coated with apolytetrafluoroethylene resin film which has been pre-processed into thesame shape as that of the electromagnetic steel plates of the statorcore 1, and the coated surface mentioned above functions as anon-adhesive treatment section 5 to prevent bonding between the statorcore 1 and the molding resin 7 to be later added. The housing 4 is alsoprovided with an agency 6 through which the coolant for cooling therotary machine is to be passed.

Next, the housing 4 into which the stator core 1 with the stator coils 2wound around it, is preheated to 100° C. and then set in a mold whichhas been heated to 150° C. beforehand. After this, a pressure of 4 MPais applied to the polyester-based molding resin that has been filledwith the powder of calcium carbonate and aluminum oxide. Thereby,similarly to embodiment 1 described above, in the housing 4, a pluralityof injection-molding gate positions 10 functioning as resin injectionports for resin-molding the housing 4 are provided circumferentially onthe side thereof so as to ensure equal injection of the resin, and thesegates are filled with the molding resin to provide injection-molding,with the result that the stator coil 2 inside the slot of the statorcore 1 and the stator coil 2 at the coil end emerging from the statorcore 1 are molded. A recess 9 for preventing the rotational vibration ofthe coil end portion is also provided in the housing 4.

As shown in FIG. 6, a shaft 21 into which a rotor 19 has been built isattached to the resin-molded stator. After this, an end plate 27 havinga bearing mounted therein is installed. The axial length (W) of a coilend space 28 provided between the resin-molded section at the coil endportion and the rear plate 27 is set to a value equal to, or greaterthan, the value derived from the product of (A×T×Lc), where A is thethermal expansion coefficient of the stator coil conductor, T is themaximum temperature that the conductor reaches during the operation ofthe rotary machine, and Lc is the total axial length of the conductorthat includes said coil end.

A stringent acceleration test for increasing the output of thethus-manufactured rotary machine from the level under its stopped statusto the maximum achievable level within a short time has been repeatedfive times, with the result that no abnormality has been observed.

1. A resin-molded stator comprising a stator core, stator coils woundaround said stator core having end faces and provided with insulation,molding resin with which the stator core and said stator coils aremolded, and a housing that stores the molding resin, wherein saidmolding resin has non-adhesive structure between the molding resin andat least one of the end faces of the stator core, and wherein an axiallength of the molding resin is shorter than an axial length of thehousing, thereby forming a space between the housing and the moldingresin.
 2. A resin-molded stator according to claim 1, wherein anon-adhesive film or separator for obtaining non-adhesion against saidresin is provided between the molding resin and at least one of the endfaces of the stator core.
 3. A resin-molded stator according to claim 1,wherein said molding resin consists of polyester resin including aninorganic filler.
 4. A resin-molded stator according to claim 3, whereinsaid inorganic filler comprises calcium carbonate and aluminum oxide. 5.A resin-molded stator according to claim 2, wherein said non-adhesivefilm is polytetrafluoroethylene resin.
 6. A resin-molded statoraccording to claim 2, wherein said separator is silicone.